I've used the Dunkelgelb Modulation Set from AK-Interactive! Despite the fact that you can use it with no dilution, I noticed that it sometimes clogs in the airbrush and I think it's a bit too thick. So, I better like to dilute it with some Lacquer Thinner from Tamiya with a proportion of 2 volumes of thinner for 1 volume of paint. It works fine, but you really have to stir the paint in order not to have a bad surprises.

I'm not a modulation pro. It's quite hard to decide which surfaces to highlight. The modulation such as we know it today has, in my opinion, nothing to deal with the zenithal technique. Of course, the highlights are on top and the shadows are beneath, but the real zenithal effect would tend to highlight all the surfaces going through the same light in the same way. However here, as you'll notice, some areas are more highlighted than others, despite being on the same level. It's rather a matter of emphasizing some volumes, rather than respecting a zenithal effect stricto sensu.

I had fun, covering some parts with masking tape, even if the paint sometimes dripped. I repeat, the paint tends to dry quickly in the airbrush, so some times when I just slightly pulled the trigger, I had an important and undesired flow of paint. I've tried to fix it as well as possible. I also didn't hesitate to reuse darker colors to add more contrast or fix some mistakes.